This application claims benefit of Japanese Applications No. 2000-75186 filed in Japan on Mar. 17, 2000 and No. 2001-29006 filed in Japan on Feb. 6, 2001, the contents of which are incorporated by this reference.
1. Field of the Invention
The present invention relates to a color image display system and a color image pickup system that use a decentered optical system. More particularly, the present invention relates to a color image display system and a color image pickup system which are adapted to electronically correct decentration chromatic aberration introduced by a decentered optical system used to display or capture a color image.
2. Description of Related Art
Various decentered optical systems have been proposed by the present applicant and so forth. The basic structure of these decentered optical systems is an optical system including one or a plurality of decentered prisms having an internally reflecting surface with a power, e.g. a rotationally asymmetric surface, decentered with respect to an optical axis. Because the reflecting and transmitting surfaces of the optical system are decentered, various decentration aberrations occur. To correct the decentration aberrations, the optical system uses at least one rotationally asymmetric surface.
Meanwhile, to correct the lateral chromatic aberration of an optical system, Japanese Patent Application Unexamined Publication (KOKAI) No. Hei-347708 proposed to display images of different colors on an image display device at respective magnifications made different from each other so that the lateral chromatic aberration is corrected.
In a decentered optical system formed from reflecting and transmitting surfaces as stated above, the reflecting surface does not produce chromatic aberration, but the entrance or exit surface of the decentered prism, which is a transmitting surface, produces not only lateral chromatic aberration but also a color shift by the dispersing prism action.
When the number of pixels of an image display device or an image pickup device is relatively small, the amount of color shift is small relative to the size of the pixels. Therefore, the color shift presents no problem. However, in the case of using an image display device or an image pickup device having a large number of pixels to provide high resolution, an image of red color and an image of blue color are viewed or captured displaced relative to each other. Thus, the resolution degrades unfavorably.
The present invention was made in view of the above-described problems with the prior art. Accordingly, an object of the present invention is to provide a color image display system and a color image pickup system, which are adapted to electronically correct the color shift of color separation images caused by a decentered optical system used to display or capture a color image.
To attain the above-described object, the present invention provides a color image display system using a decentered optical system. The color image display system has an image display apparatus including a color image display device for displaying a color image composed of color separation images superimposed on one another. The color image displayed on the color image display device is projected into an eyeball of an observer through a viewing optical system. The viewing optical system is formed from a decentered optical system including a decentered prism having at least a decentered internally reflecting surface with a power, together with an entrance surface and an exit surface, which are transmitting surfaces, respectively.
In the image display apparatus, the pixel position of each color separation image to be displayed on the color image display device is shifted so as to cancel a color shift of the corresponding color separation image caused by the decentered optical system.
In this case, it is preferable that the color image display device be arranged to display each color separation image by a set of scanning lines in the horizontal scanning direction, and that the pixel position be shifted only in the direction of the scanning lines. With this arrangement, no field memory is needed, and the electronic circuit can be simplified in structure. At the same time, it becomes possible to correct more than half of lateral chromatic aberration occurring in the optical system.
If the plane of symmetry of the decentered prism and the direction of the scanning lines are set parallel to each other, it becomes possible to correct a color shift due to the decentration of the decentered prism by producing a color shift in the direction of the scanning lines. In a case where the color image display device has a laterally long image display area with a ratio of 16:9, in particular, the lateral direction of the image display area should preferably be set parallel to the plane of symmetry of the decentered prism. By doing so, even more advantageous effects can be obtained.
In addition, the present invention provides a color image pickup system using a decentered optical system. The color image pickup system has an image pickup apparatus including a color image pickup device for capturing a color image and outputting color separation image signals. An image pickup optical system forms an object image on the color image pickup device. The image pickup optical system is formed from a decentered optical system including a decentered prism having at least a decentered internally reflecting surface with a power, together with an entrance surface and an exit surface, which are transmitting surfaces, respectively.
In the image pickup apparatus, the pixel position of each color separation image signal outputted from the color image pickup device is shifted so as to cancel a color shift of the corresponding color separation image caused by the decentered optical system.
The operation of the present invention will be described below.
In a decentered optical system, tilted optical surfaces are formed from rotationally asymmetric surfaces to fold an optical path, thereby allowing the optical system to be constructed in a compact form. If the optical system is formed from a decentered prism and a surface having an optical power is formed from an internally reflecting surface (back-coated mirror) of the decentered prism, it is possible to construct an optical system free from chromatic aberration, in particular.
Such an internally reflecting surface produces no chromatic aberration in theory. However, because the optical path is bent, the amount of decentration aberrations produced increases. The decentration aberrations can be corrected by a rotationally asymmetric surface.
In such a decentered prism, at least two transmitting surfaces are present, i.e. an entrance surface through which light enters the prism, and an exit surface through which light exits the prism. Chromatic aberration produced by the entrance and exit surfaces cannot be corrected unless another optical system is used. The reason for this is that because the reflecting surface does not produce chromatic aberration, there is no surface capable of correcting the chromatic aberration produced by the transmitting surfaces.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.